258 Scientific Intelligence. 



6. The Radiometer for Measurement of Low Pressures. — Prof. 

 J. Dewar finds that this instrument is available for the measure- 

 ment of extremely low pressures. It is well known that the 

 McLeod gauge is not very reliable for measurements below one- 

 thousandth of a millimeter. Professor Dewar, by the use of his 

 well-known methods of the use of charcoal combined with liquid 

 air, found that the radiometer indicated pressures as low as 

 "ST.tot.too" °f an atmosphere. — Proc. Roy. Soc. (A), lxxix, pp. 

 529-532, 1907. J. T. 



7. Existence of Positive Electro?is in the Sodium Atom. — 

 Prof. R. W. Wood finds two tjqaes of magnetic rotation in the 

 channeled spectrum of sodium vapor, and believes that these 

 two types indicate the presence of positive and negative electrons 

 in the atom. — Phil. Mag., Feb., 1908, pp, 274-279. J. t. 



8. Magnetic Effect of Cathode Rays. — It is well known that 

 a magnet easily deflects a stream of cathode rays. This effect is 

 explained by the fact that the rapid movement of charged 

 particles constitute an electric current. Eugen Klttpathy 

 shows that the converse is true, that the stream of cathode rays 

 can produce a magnetic effect. — Ann. der Physik, No. 1, 1908, 

 pp. 31-47. J. t. 



9. Practical Physics ; by W. S. Franklin, C. M. Crawford 

 and Barry Macnutt. Vol. I. Precise Measurements. Measure- 

 ments in Mechanics and Heat. Pp. vi+172. Vol. II. Elemen- 

 tary and Advanced Measurements in Electricity and Magnetism. 

 Pp. vi+160. Vol. HI. Photometry, Experiments in Light and 

 Sound. Pp. vii + 80. New York, 1 908. (The Macmillan Co")— This 

 laboratory manual for students in colleges and technical schools 

 contains a well-chosen list of instructive and interesting experi- 

 ments ; the descriptions of apparatus and the directions for 

 carrying out the experiments are clear and practical. The sug- 

 gestions as to the calculation and presentation of results and the 

 estimation of errors are also to be commended. h. a. b. 



10. PraJctische Photometrie ; by Emil Liebenthal. 8vo, 

 445 pp., 201 figures. Braunschweig, 1907 (F. Vieweg u. Sohn). — 

 This book owes its excellence to the fact that its writer has had 

 many years experience in photometric investigations conducted 

 in the laboratory of the Physikalisch-Technische Reichsanstalt 

 at Charlottenburg. The author has treated all phases of the 

 subject in great detail and has endeavored to express the ideas 

 in language comprehensible to the non-scientific, practical reader 

 and yet, at the same time, rigorous enough to satisfy the require- 

 ments of the student of pure science. Numerical examples are 

 given throughout to illustrate the use of the principles and for- 

 mulae previously discussed. The special subject of spectropho- 

 tometry has only seventeen pages devoted to it because the 

 author does not consider that it properly comes under the title of 

 u Practical Photometry." The wealth of late, accurate, numeri- 

 cal data contained in the text and appended tables will undoubt- 

 edly make the book very useful for reference. h. s. tj. 



